I'm not so sure. He thinks the artifacts at Calico were man-made.
Calico: A 200,000 Year Old Site In America
"(1) the authenticity of the artifacts; are they truly the product of human manufacture, or merely naturally produced "geofacts?" and (2) the obvious pre-Clovis age of the deposits (see, for example, lengthy discussions in Leakey and others, 1968; Haynes, 1973; Bryan, 1978; Taylor and Payen, 1975; Carter, 1980; Meighen, 1983; Patterson, 1983; and Budinger and Simpson, 1985)."
If I remember correctly Leakey thought that there could have been preclovis settlement in the New World. I was surprised at the thought, he may have been wrong in the details but he was one of the first to suggest that the settlement of NA predated Clovis.
Louis Leakey (the old, dead guy) caught hell for talking about greater antiquity than the (at that time) dogma of 3000 years (IOW, the blind belief back then was that humans had entered the Americas no more than 3000 years ago). This was before Clovis entered the picture. He based that on the number of major civs found around the two continents, the number of language families, etc. Since that time, Clovis-First-and-Only replaced the 3000 year limit.